A great number of halogenated aromatic compounds pose a major environmental pollution problem due to their toxicity and resistance to degradation by natural sources. These were introduced into the environment by a variety of routes--some intentionally, some by accident, and some as accidental contaminants in other compounds deliberately spread as insecticides or defoliants, for example. This proposal describes a new technique which will lead to a greatly enhanced ability to degrade these compounds, focusing attention on polychlorinated biphenyls (PCB's), polybrominated biphenyls (PBB's), chlorinated terphenyls, chlorinated dioxins, chlorinated phenols, and similar halogenated aromatic compounds. The new technique for detoxification of these materials relies on a photochemical dehalogenation, performed in the presence of hydride donors, which greatly accelerate the rate of the dehalogenation reaction. The proposal seeks to establish the general utility of this new method, and describes steps to optimize the reaction conditions by systematically varying the solvent, concentration, temperature, and nature of the hydride source.